WASHINGTON (Reuters) - The U.S. Supreme Court’s conservative majority on Tuesday appeared poised to hand President Donald Trump a victory on his administration’s plan to add a citizenship question to the 2020 census, a move opponents call a Republican effort to deter immigrants from taking part.

Conservative justices signaled during arguments in the closely watched case a willingness to overturn a lower court ruling that blocked the question and appeared untroubled by the administration’s stated justification for using the citizenship question in the decennial population count. Their liberal counterparts expressed hostility toward allowing the question.

The court has a 5-4 conservative majority and has backed Trump in other high-profile cases. Conservative justices indicated a citizenship question would be eminently reasonable, noting that other countries use such questions and that the United States has done so in the past in one form or another.

Among the conservative justices indicating support for the administration’s stance were Trump’s two appointees, Brett Kavanaugh and Neil Gorsuch, and Chief Justice John Roberts, considered the court’s pivotal vote.

Opponents have said the question would cause a sizeable undercount by frightening immigrant households and Latinos from filling out the census forms, fearful that the information would be shared with law enforcement. This would cost Democratic-leaning areas electoral representation in Congress and federal aid, benefiting Trump’s fellow Republicans and Republican-leaning parts of the country, they said.

The census is used to allot seats in the U.S. House of Representatives and distribute some $800 billion in federal funds.

Lower courts ruled that the administration violated federal law and the U.S. Constitution in seeking to include the question on the census form. A ruling by the Supreme Court is due by the end of June.

During about 80 minutes of arguments, Roberts and other conservative justices appeared to accept the administration’s argument that the question would yield better data to enforce the Voting Rights Act, which protects eligible voters from discrimination.

Roberts told New York Solicitor General Barbara Underwood, whose state sued to block the question, that citizenship data is critical for enforcing the Voting Rights Act and said it was “quite common” for the census to capture demographic details.

Kavanaugh said it is a “very common question” internationally, and that federal law gives Commerce Secretary Wilbur Ross, whose department includes the Census Bureau, “huge discretion” in how the survey is conducted.

The Supreme Court already has handed Trump some major victories, including upholding his travel ban targeting people from several Muslim-majority countries in June 2018. The court in January let Trump’s policy barring many transgender people from the U.S. military to go into effect.

The census case comes in a pair of lawsuits by a group of states and localities led by New York state, and a coalition of immigrant rights groups challenging the legality of the question. The census forms are due to be printed in the coming months.

‘A CONTRIVED ONE’

Liberal justices noted evidence presented by the Census Bureau’s own experts that showed the citizenship question would lead to a population undercount, and, contrary to the administration’s stated goal, less accurate citizenship data.

They also voiced skepticism about the administration’s Voting Rights Act justification.

“You can’t read the record without sensing that this need is a contrived one,” liberal Justice Elena Kagan said.

“This is a solution in search of a problem,” added liberal Justice Sonia Sotomayor, the court’s only Hispanic justice.

Sotomayor, who tangled with Trump administration’s lawyer Noel Francisco during the argument, said there was “no doubt” the question would drive down the census response rate.

But Gorsuch and fellow conservative Justice Samuel Alito challenged evidence that inquiring about citizenship could lower response rates. Gorsuch noted that “it’s not like this question is improper to ask.”

Francisco argued that Ross acted properly within his discretion in deciding to add the question, adding, “It really does boil down to whether the secretary’s judgment here is a reasonable one.”

Citizenship has not been asked of all households since the 1950 census. It has featured since then on questionnaires sent to a smaller subset of the population. While only U.S. citizens can vote, non-citizens comprise an estimated 7 percent of the population.

Manhattan-based U.S. District Judge Jesse Furman on Jan. 15 ruled that the Commerce Department’s decision to add the question violated a federal law called the Administrative Procedure Act. Federal judges in Maryland and California also prohibited the question’s inclusion in subsequent rulings, saying it would violate the Constitution’s mandate to enumerate the population every 10 years.

The Census Bureau estimated that households corresponding to 6.5 million people would not respond to the census if the citizenship question is asked.

Immigrant advocacy groups rallied outside the court after the argument, with demonstrators carrying signs reading “no census without us” and “fair and accurate count for all.”

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U.S. Representative Carolyn Maloney, a Democrat who represents part of New York City, said, “I hope the justices feel strongly that the Constitution should be upheld, that the science should be upheld, and that the experts should be listened to.”